The present invention relates to a process for manufacturing a semi-finished product with circular knitting machines, in particular for producing undershirts, one-piece body garments, briefs or the like.
As known, tubular knitted products manufactured with circular knitting machines are used to produce undershirts with no lateral seams. Said products have a substantially uniform knitting along their entire extension, except for any possible ornamental patterns, and in order to produce undershirts they are first cut according to the required length, and four portions are subsequently removed at a longitudinal end of the product so as to respectively define the front and back neck-openings and the openings for the arms. When these four portions are removed, four flaps are defined and are subsequently sewn together in pairs so as to obtain the shoulders of the undershirt.
A finishing border is applied along the cutting lines for the removal of the four portions, and the lower end of the undershirt is subjected to a hemming operation with the possible application of an elastic strip.
With this process, the waste consequent to the removal of the portions corresponding to the neck and arm openings considerably affect production costs, since the thread used for this kind of product is generally of high quality.
The cutting operations furthermore generally require the use of templates in order to obtain sufficiently precise results, and imply relatively long times and in turn affect production costs.
Semi-finished products for producing briefs are also known which are also manufactured with particular circular machines which are similar to circular knitting machines for manufacturing socks and stockings, but with an enlarged needle cylinder.
A first kind of product is manufactured by means of a process which substantially consists in initially providing an elastic hem and, after said hem, a section of tubular knitting, using nearly all the needles of the needle cylinder. In a subsequent step, an increasing number of needles belonging to two sets of needles are excluded from knitting; said sets of needles are angularly mutually spaced with respect to the axis of the needle cylinder so as to define, on the lateral surface of the product, two missing portions which correspond to the leg opening of the briefs to be produced. The number of needles excluded from knitting gradually increases up to a maximum value to obtain a widening of the leg openings and to obtain such a length of the portions between the two missing portions as to allow their overlapping and sewing to obtain the crotch of the briefs. The thread or threads are cut, at the beginning of the sets of needles which are not knitting, i.e. at the edges of the leg openings, by means of appropriate devices fitted to the circular knitting machine being used.
The product is finished by applying an elastic tape or lace to the edge which delimits the leg openings and by sewing the overlapping ends of the portions of knitting arranged between the two missing portions so as to provide, as mentioned, the crotch of the briefs.
However, this known type of product is not devoid of disadvantages, not least of which is the fact that flaws or ladders often form at the leg openings and propagate along the knitted fabric. Such flaws most frequently occur during the final stages of manufacturing the product i.e., when subjecting the product to pneumatic tensioning, during expulsion of the product from the knitting machine, or when applying elastic tape to the edges of the leg openings. Obviously, the presence of such flaws results in the product being rejected.
A second kind of product is manufactured with a process which instead of cutting the threads at the edge of the leg openings obtains a complete tubular product, and two portions knitted with different stitches with respect to those used for the remaining part of the product are provided at the leg openings, or stitches are knitted along lines corresponding to the border of the leg openings, so as to allow the easy identification of the portions to be successively cut in order to provide the leg openings.
Knitting with different stitches of the entire portions to be removed or the delimiting thereof by means of a line knitted with different stitches with respect to the remaining part of the product allows greater precision and speed in the product finishing operations.
This process safely excludes the possibility of broken meshes, flaws or ladders before the finishing oeprations, but has the disadvantage of requiring considerable waste for each product.